Wearing a mask is about not spreading your droplets around. While they do protect you to some degree they also protect other people from you. There is no way to know if you are an asymptomatic or presymptomatic carrier. Hand washing and sterilization are also useful tools but so are masks. Certainly we need to have them for our providers but having even a cotton bandanna on yourself is a courtesy to others. Anything to reduce your spread of droplets may help others.